GHSA-3696-VCMQ-4G83
Vulnerability from github – Published: 2025-07-10 09:32 – Updated: 2025-11-18 15:30In the Linux kernel, the following vulnerability has been resolved:
fs/nfs/read: fix double-unlock bug in nfs_return_empty_folio()
Sometimes, when a file was read while it was being truncated by
another NFS client, the kernel could deadlock because folio_unlock()
was called twice, and the second call would XOR back the PG_locked
flag.
Most of the time (depending on the timing of the truncation), nobody
notices the problem because folio_unlock() gets called three times,
which flips PG_locked back off:
- vfs_read, nfs_read_folio, ... nfs_read_add_folio, nfs_return_empty_folio
- vfs_read, nfs_read_folio, ... netfs_read_collection, netfs_unlock_abandoned_read_pages
- vfs_read, ... nfs_do_read_folio, nfs_read_add_folio, nfs_return_empty_folio
The problem is that nfs_read_add_folio() is not supposed to unlock the folio if fscache is enabled, and a nfs_netfs_folio_unlock() check is missing in nfs_return_empty_folio().
Rarely this leads to a warning in netfs_read_collection():
------------[ cut here ]------------ R=0000031c: folio 10 is not locked WARNING: CPU: 0 PID: 29 at fs/netfs/read_collect.c:133 netfs_read_collection+0x7c0/0xf00 [...] Workqueue: events_unbound netfs_read_collection_worker RIP: 0010:netfs_read_collection+0x7c0/0xf00 [...] Call Trace: netfs_read_collection_worker+0x67/0x80 process_one_work+0x12e/0x2c0 worker_thread+0x295/0x3a0
Most of the time, however, processes just get stuck forever in
folio_wait_bit_common(), waiting for PG_locked to disappear, which
never happens because nobody is really holding the folio lock.
{
"affected": [],
"aliases": [
"CVE-2025-38338"
],
"database_specific": {
"cwe_ids": [
"CWE-415"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-07-10T09:15:28Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nfs/nfs/read: fix double-unlock bug in nfs_return_empty_folio()\n\nSometimes, when a file was read while it was being truncated by\nanother NFS client, the kernel could deadlock because folio_unlock()\nwas called twice, and the second call would XOR back the `PG_locked`\nflag.\n\nMost of the time (depending on the timing of the truncation), nobody\nnotices the problem because folio_unlock() gets called three times,\nwhich flips `PG_locked` back off:\n\n 1. vfs_read, nfs_read_folio, ... nfs_read_add_folio,\n nfs_return_empty_folio\n 2. vfs_read, nfs_read_folio, ... netfs_read_collection,\n netfs_unlock_abandoned_read_pages\n 3. vfs_read, ... nfs_do_read_folio, nfs_read_add_folio,\n nfs_return_empty_folio\n\nThe problem is that nfs_read_add_folio() is not supposed to unlock the\nfolio if fscache is enabled, and a nfs_netfs_folio_unlock() check is\nmissing in nfs_return_empty_folio().\n\nRarely this leads to a warning in netfs_read_collection():\n\n ------------[ cut here ]------------\n R=0000031c: folio 10 is not locked\n WARNING: CPU: 0 PID: 29 at fs/netfs/read_collect.c:133 netfs_read_collection+0x7c0/0xf00\n [...]\n Workqueue: events_unbound netfs_read_collection_worker\n RIP: 0010:netfs_read_collection+0x7c0/0xf00\n [...]\n Call Trace:\n \u003cTASK\u003e\n netfs_read_collection_worker+0x67/0x80\n process_one_work+0x12e/0x2c0\n worker_thread+0x295/0x3a0\n\nMost of the time, however, processes just get stuck forever in\nfolio_wait_bit_common(), waiting for `PG_locked` to disappear, which\nnever happens because nobody is really holding the folio lock.",
"id": "GHSA-3696-vcmq-4g83",
"modified": "2025-11-18T15:30:41Z",
"published": "2025-07-10T09:32:31Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-38338"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/14f5549ad163be2c018abc1bb38370fff617a243"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1e93b61d3eaa14bfebcc2716ac09d43f3845d420"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4c10fa44bc5f700e2ea21de2fbae520ba21f19d9"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5bf0b9eeb0174686f22c2e5b8fb9f47ad25da6f5"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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